In the past year, we have continued to study a series of serum samples in the following 4 categories: (1) High HDL-C (>80 mg/dL) with cardiovascular disease (CHD) (N=58), (1) High HDL-C (>80 mg/dL) with no CHD (N=58), (1) Low HDL-C (< 30 mg/dL) with CHD (N=47), (1) Low HDL-C (< 30 mg/dL) with no CHD (N=58). All subjects have LDL-C< 130 mg/dL and are on no lipid lowering medications.[unreadable] [unreadable] Pre-beta HDL, a small size HDL subfraction, was measured by an ELISA and its level was 2-3 fold higher in subjects with CHD in both the high (p<0.0001) and low HDL-C (p=0.001) groups. Interestingly, LCAT, a serum enzyme involved with the maturation and lipidation of HDL, was found to be significantly lower in activity in the same subjects with CHD and high (p=0.002) or low (p=0.03) HDL-C. Receiver operating characteristic curve of pre-beta HDL for predicting CHD in the high HDL-C groups yielded an area under curve of 0.71, which increased to 0.92 when LCAT values were included. Similar results were obtained for the low HDL-C groups. A strong inverse correlation between LCAT activity and pre-beta HDL-C (r2=0.30, p<0.0001), which was especially strong in the low HDL-C group (r2=0.56, p<0.0001, was observed. [unreadable] [unreadable] Subjects with high HDL-C and CHD also had approximately 15% more apoA-I (p=0.001) and apoA-II (p=0.002) and nearly 10% more phospholipid (p=0.007) on their HDL than subjects with similar HDL-C and no CHD. Likewise, the group with low HDL-C had 30% more apoE (p=0.035) and approximately 10% more phospholipid (p=0.047) than the group with similar HDL-C levels and no CHD.[unreadable] [unreadable] [unreadable] In summary, CHD subjects showed modest compositional differences in the protein and lipid content of HDL; however, the much greater differences observed in HDL subfraction analysis and in LCAT activity suggest that these markers may improve CHD risk prediction. It also suggests that patients at risk for CHD may have defects in their ability to efflux cholesterol from peripheral cells to HDL, which results in the decreased conversion of pre-beta HDL to the larger HDL subfractions. Future studies will be aimed in examining these relationships in other patient populations and to assess the possible clinical utility of these tests for predicting CHD.